A diffusion transfer process utilizing silver salts such as silver halide, etc., has been known. In such a photographic process, it is known that positive silver images are obtained directly on an image receiving element by putting a light-sensitive element containing an exposed silver halide photographic emulsion on an image receiving element containing silver precipitants and processing in the presence of a developing agent by applying an alkaline processing solution containing a silver halide solvent between these two elements.
According to this process, unexposed silver halide emulsion in the light-sensitive element is dissolved by the silver halide solvent and enters the alkaline processing solution as a silver ion complex which is transferred to the image receiving element, wherein it precipitates as a silver image by the action of the silver precipitants, and, consequently, direct positive images are formed.
The image receiving element used in this process is generally produced by providing an image receiving layer which contains silver precipitants selected from metal sulfides such as nickel sulfide, silver sulfide or palladium sulfide, etc., and noble metal colloids such as gold, silver, palladium, etc., in an alkali permeable polymer binder selected from gelatin, carboxymethyl cellulose, hydroxyethyl cellulose, regenerated cellulose, polyvinyl alcohol, sodium alginate, starch, gum arabic and colloidal silica, etc., on a paper support such as baryta paper, polyethylene laminated paper, lacquer paper or synthetic paper, etc., or a film support such as an acetyl cellulose film, a polyethylene terephthalate film or a polystyrene film, etc.
In order to improve image receiving elements, numerous inventions have been made. Particularly, it has been known to use regenerated cellulose as a binder in the image receiving layer.
In U.S. Pat. No. 3,179,517, a process is described for producing image receiving elements which comprises forming a regenerated cellulose layer by hydrolyzing an acetyl cellulose film with an alkali, and thereafter immersing the regenerated cellulose layer in a solution of a gold salt and a solution of a reducing agent to cause a reaction in the layer, whereby a gold colloid silver precipitant is formed.
Japanese Patent Publication No. 32754/69 teaches producing an image receiving element by a process which comprises incorporating a silver precipitant in an alkali impermeable polymer substance by vacuum deposition, dissolving it in a solvent which dissolves the polymer substance, applying the resulting solution to a support, drying and hydrolyzing the surface layer of the formed polymer layer so as to render the same alkali permeable.
Japanese Patent Publication No. 43944/71 discloses producing an image receiving element by a process which comprises forming silver precipitants in a solution of acetyl cellulose, applying it to a support and hydrolyzing acetyl cellulose to convert it into regenerated cellulose.
Japanese Patent Publication No. 49411/76 discloses preparing an image receiving element by a process which comprises hydrolyzing a cellulose ester layer and incorporating silver precipitants in the hydrolyzed layer simultaneously with or after hydrolysis.
U.S. Pat. No. 4,163,816 discloses the production of an image receiving element by a process which comprises hydrolyzing acetyl cellulose in a solution with an acid to convert it into acetyl cellulose having a low degree of acetylation, and applying the solution to a support.
However, silver images formed on the image receiving elements obtained as described above have the faults in that they easily discolor or fade during preservation.
As a process for improving the above described faults, it is disclosed in Japanese Patent Publication No. 5392/71, U.S. Pat. No. 3,533,789 and British Pat. No. 1,164,642 that one can apply a water-soluble polymer solution containing an alkali neutralizing component to the surface of the resulting silver images. However, according to this process, the surface to which the aqueous solution of the polymer is applied requires a long time for complete drying. Therefore, it is impossible to arrange the prints in layers while drying, because the surface is sticky, and thus fingerprints and dust often adhere to the surface. Further, application of such a solution to silver images is troublesome.
Japanese Patent Publication No. 44418/81 discloses image receiving elements comprising a support, (I) a hydrolyzable cellulose ester, polyvinyl ester or polyvinyl acetal layer containing a diffusible compound capable of changing the properties of silver images, which becomes to have an alkali-permeable property by hydrolysis, provided on the support, and (II) a regenerated cellulose layer containing silver precipitants provided on the above described layer. As the diffusible compounds capable of changing the properties of silver images, organic mercapto compounds are disclosed. In this case, the diffusion transfer processing solution and the mercapto compound in layer (I) gradually diffuse into layer (II) and protect silver images formed in layer (II), whereby discoloration and fading can be prevented.
In order to completely exhibit the effect of preventing discoloration and fading, it is necessary that the mercapto compound has sufficient ability to prevent discoloration and fading and remains in layer (I) during storage of the undeveloped image receiving element or during diffusion transfer processing, but that it permeates into layer (II) from layer (I) after formation of silver images by diffusion transfer processing to protect the images formed on layer (II). If the mercapto compound diffuses into layer (II) from layer (I) before conclusion of diffusion transfer processing, development is restricted and the optical density of the transferred silver image on the image receiving material deteriorates on the whole. Further, if diffusion of the mercapto compound is retarded too much, discoloration or fading of images occurs before the silver images are protected by the mercapto compound.
However, the mercapto compounds described in Japanese Patent Publication No. 44418/81 have faults in that they have insufficient ability to prevent discoloration and fading and may cause discoloration or fading of images, and further they restrain development by diffusing into layer (II) from layer (I) during storage of the undeveloped image receiving element to deteriorate the optical density of the transferred silver images.
Japanese Patent Application (OPI) No. 120634/74 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses image receiving elements which are produced using homopolymers, copolymers and graft polymers of a monoacrylate or monomethacrylate of a polyhydric alcohol as a polymer layer containing a compound which changes the properties of silver images.
However, the compounds disclosed in Japanese Patent Application (OPI) No. 120634/74 have faults similar to those of the compounds disclosed in Japanese Patent Publication No. 44418/81, i.e., they have insufficient ability to prevent discoloration or fading of images and they cause a decrease in the optical density of transferred silver images.
British Pat. No. 1,276,961 discloses that 2-mercapto-1,3,4-triazole derivatives can be used for obtaining stable silver images by a diffusion transfer process and U.S. Pat. No. 3,655,380 discloses that 5-seleno-1,2,3,4-tetrazole derivatives improve the tone of silver image obtained by a diffusion transfer process so as to be neutral gray and they give stable silver images.
However, these compounds have a fault in that the effect of stabilizing silver images obtained by a diffusion transfer process is insufficient to prevent discoloration or fading of images.
Therefore, it has been desired to provide compounds having a good effect of stabilizing silver images.